Human oral mucosal lesions of a keratotic nature are studied clinically and histologically over their duration for changes occurring in them. Lesions studied include hyperplastic, pre-malignant, and inherited mucosal disorders. Each case undergoes a detailed environmental analysis, appropriate laboratory studies are performed, and a record of the clinical and histologic changes is obtained in order to document the clinicopathologic progression of the disease. Where indicated, appropriate correlative studies, such as histochemistry, electron microscopy, biodynamic (turnover) studies, immunofluorescent procedures, etc., are employed to provide additional significant data.